The widespread use of semiconductors is due to their usefulness, their cost effectiveness and to their unique capabilities. Accompanying the growth in the use, and usefulness, of semiconductors is the development of new processes and materials for the design and manufacture of semiconductors together with new or improved manufacturing equipment and hardware. An important recent development is the use of copper (which has about twice the unit conductivity of more commonly used aluminum) for electrical interconnections, or circuit traces within very large scale integrated circuits (VLSIs). The use of copper has permitted faster speeds of operation and greater capability of the VLSI circuits but has led to the need to prevent atoms of copper in the copper circuits from adversely interacting with atoms of other materials used in the VLSIs. One way of preventing such interactions is to provide a "barrier" layer over and/or under the copper, such as a thin layer of tungsten (W).
It is known that a layer of a material such as tungsten can be deposited by chemical vapor deposition (CVD) onto exposed surfaces of a semiconductor wafer during processing into VLSIs. Tungsten, which is a relatively heavy metal having an atomic weight of 183.86, has high temperature resistance and provides suitable protection against the reaction of copper with other materials during the fabrication of VLSIs. A compound of tungsten, namely tungsten hexacarbonyl [W(CO).sub.6 ], can be vaporized under suitable conditions of pressure and temperature to obtain a gaseous phase of the compound which can then be used in CVD processing to form a film or layer of metallic tungsten on a semiconductor wafer. This will be explained in greater detail hereinafter.
It is desirable that a layer of metal (such as tungsten) being deposited by CVD on a semiconductor wafer be uniform in thickness. To achieve this, a chemical vapor compound of the material flowing into a reaction chamber where the semiconductor wafer is being processed should be controlled in flow direction and amplitude so that the vapor is evenly distributed and flows uniformly toward the wafer. This is especially true of a material such as tungsten hexacarbonyl vapor, the molecules of which have relatively high weight and inertia. In addition, because a CVD process step using a compound such as tungsten hexacarbonyl is typically carried out in a reaction chamber maintained under low pressure conditions (e.g., a small fraction of a Torr), the flow of gas vapor into the chamber through a dispersion plate should have high-flow-conductance so that pressure drop across it is relatively low. The gas vapor should also be controlled in temperature as it passes through the plate and enters the chamber to prevent condensation of the vapor.
It is desirable to have a simple and efficient dispersion plate which fills the above described needs.